My set of 5 12" Mistral wheels only has 3 caps between them and I'd REALLY like to make it 4. Please have a look around your projects, collection of parts, collection of Minis Metros and everything else you may have kicking about. I realise this may be a total long shot, but someone must have one somewhere? They look like this & are metal:
Drop me a PM if you have anything. Thanks!